Apparatus for operating electric discharge lamps

ABSTRACT

There is disclosed an improved discharge lamp lighting apparatus having a first semiconductor switching element connected in series with the discharge lamp and a second semiconductor switching element connected in parallel with the discharge lamp. A control circuit included in the lighting apparatus for switching on the first and second semiconductor switching elements alternately to light and operate the discharge lamp at a high frequency and prevents short circuit fault of the electric power source due to a simultaneous on-condition of two switching elements by imparting a time interval longer than the turn-off time of the first and second semiconductor switching elements between two pulses respectively driving the first and second switching elements.

United States Patent Nomura et a1.

[15] 3,657,598 Apr. 18, 1972 Inventors:

[72] Osamu Nomura; Fumio Kamiya, both of Yokohama, Japan Tokyo Shibaura Electric Kawasaki-shi, Japan Nov. 5, 1970 Assignee: Co., Ltd.,

[30] Foreign Application Priority Data Nov. 11, 1969 Japan ..44/89749 [56] References Cited UNITED STATES PATENTS 3,265,930 8/1966 Powell, Jr. ..315/207 Primary Examiner-John Kominski Attorney-Flynn & Frishauf ABSTRACT There is disclosed an improved discharge lamp lighting apparatus having a first semiconductor switching element connected in series with the discharge: lamp and a second semiconductor switching element connected in parallel with the discharge lamp. A control circuit included in the lighting apparatus for switching on the first and second semiconductor switching elements alternately to light and operate the discharge lamp at a high frequency and prevents short circuit fault of the electric power source due to a simultaneous oncondition of two switching elements by imparting a time interval longer than the tum-off time of the first and second semiconductor switching elements between two pulses respectively driving the first and second switching elements.

PATENTED '1 @72 I SHEET 10F 7 TIME All MODE ESE B F IG. 2

APPARATUS FOR OPERATING ELECTRIC DISCHARGE LAMPS The present invention relates to an apparatus for lighting a discharge lamp, and more particularly to an improvement of a control circuit utilized in the lighting apparatus.

As diagrammatically shown. in FIGS. 16 and 17 of the drawings of U5. Pat. No. 3,265,930, according to a prior art apparatus for lighting the discharge lamp, a series circuit including a first bidirectional semiconductor switching circuit, a reactance element, a discharge lamp, and a feedback resistor are connected across an AC. source and a second bidirectional semiconductor switching circuit is connected across a juncture between the first switching circuit and the reactance element and a juncture betweenone terminal of the A.C. source and the feedback resistor.

The first and second switching circuits are rendered alcircuit is rendered conductive, that is, on-state, whereas the second switching circuit is rendered non-conductive, that is, off-state, and thus the A.C. source supplies current to the discharge lamp. When the current flows through the lamp, th'e reactance element stores energy, and a voltage drop is created across the feedback resistor. In response to this voltage drop, the control circuit functions to switch off the first switching circuit and to switch on the second switching circuit. At this time, the energy stored in the reactance element is supplied to the lamp via the second switching circuit.

Thereafter, the above described operation is repeated and the apparatus operates at a high frequency of more than several kHz.

However, in actual operation, the above described prior apparatus often results in the short-circuit failure of the source due to the presence of a simultaneous on-state of the first and second switching circuits which, of course, should be rendered on and off alternately.

It is, accordingly, an object of this invention to provide an improved control circuit utilized in the apparatus for lighting discharge lamps so as to eliminate the short-circuit failure of the source described above.

According to this invention, there is provided an apparatus for an electric lighting discharge lamp comprising a power source, a first semiconductor switching element and a reactive impedance element and a discharge lamp which are connected in series across the source, and a second semiconductor switching element connected in parallel across the series connection of the discharge lamp and reactive impedance element.

Further, a control circuit is provided which generates two pulse sequences for alternately switching on and off the first and second semiconductor switching elements and includes means to impart a time interval longer than the turn-off time of the first and second semiconductor switching elements between pulses of the two pulse sequences.

The present invention can be more fully understood from the following detailed description when taken in connection with the accompanying drawings, in which:

FIG. I is a known transistor switching circuit diagram;

FIG. 2A is a waveform diagram of current flowing into the base of the transistor of a switching circuit shown in FIG. 1;

FIG. 2B is a waveform diagram of the collector voltage of the transistor of the switching circuit shown in FIG. 1;

FIG. 3A is a circuit diagram of the apparatus for lighting discharge lamps according to one embodiment of this invention wherein two switching transistors are utilized;

FIG. 3B is a circuit diagram of the apparatus for lighting discharge lamps which employs two thyristors as switching elements instead of transistors;

FIG. 4 is a block diagram of a control circuit according to one embodiment of this invention;

FIG. 5 is a series of wavefonns provided for explanation of the control circuit shown in FIG. 4;

FIG. 6 shows waveform diagrams showing the time relationship betweeh the base current of a transistor and the lamp current in the case where the control circuit shown in FIG. 4 is utilized in the'lighting apparatus shown in FIG. 3;

FIG. 7 is a block diagram of a control circuit according to another embodiment of this invention;

FIG. 8 is a series of waveform diagrams useful in explaining the operation of a control circuit shown in FIG. 7;

FIG. 9 is a block diagram of a control circuit according to still another embodiment of this invention;

FIG. 10 is a series of waveform diagrams for explaining the operation of a control circuit shown in FIG. 7;

FIG. 11 is a block diagram of a control circuit according to further embodiment of this invention; and

FIG. 12 shows waveform diagrams for explaining the operation of a control circuit shown in FIG. 11.

Referring to FIGS. 1 and 2, a transistor switching circuit and its operation will be explained.

In FIG. I, the reference numeral 1 indicates an NPN type transistor, for instance, having the emitter grounded, and the collector of transistor 1 is connected by a resistor 2 to a positive terminal 3 of DO source and the base of transistor 1 is grounded by a secondary winding 5 of a pulse transformer 4. A primary winding 6 of pulse transformer 4 has one terminal grounded and on another terminal 7 is impressed a rectangular wave pulse voltage, for instance.

When the primary winding of the pulse transformer 4 is impressed by the rectangular pulse voltage having a voltage value sufficiently large to saturate the transistor 1, current having a waveform shown in FIG. 2A flows into the base of transistor 1. The collector voltage Vc varies with the base current as shown in FIG. 2B.

That is to say, the collector current begins to flow with time delay td after the supply of base current ib, and the collector current increases during time rr until the collector voltage Vc is saturated and drops substantially to the zero level.

The time Id is referred to as delay time" and the time tr as rising time respectively.

Subsequently, when the base current reaches instantaneously to the zero value as the input pulse supply is interrupted, the base current flows in the reverse direction because of the transformer coupling. As the result, the collector voltage Vc slightly rises during the time rs and then rapidly rises during the time If while the collector current reduces. The time ts is referred to as storage time, and the time if as falling time."

As described above, when the transistor is driven into a saturated condition, the collector voltage and hence the collector current varies with come time delay as compared with the input voltage. The sum of time rd and time tr is called turn-on time r and the'sum of time ts and time if is called turn-off time t n. There is generally a. relationship t t for transistors and this accounts for the short-circuit failure of the prior art described above.

Following is the explanation of a lighting apparatus according to this invention which employs a semiconductor switching element having the above-mentioned operation characteristic, FIGS. 3A and 3B being referred to.

Referring to FIG. 3A, the reference numeral 10 denotes a suitable D.C. source represented by a battery. It will be ap parent that the DC. source may be a rectified alternating current supply.

Across the power source 10 is connected a series circuit including a first transistor 11 of NPN type having a control electrode or base electrode, a reactance element 12 (a condenser in this case, otherwise an inductor), and a discharge lamp 13. The NPN type transistor 11 is connected in the forward direction with respect to the polarity of source 10. The collector of transistor 11 is directly connected to the positive terminal of the source and the emitter is connected to one terminal of the condenser 12.

Further, a second NPN type transistor 14 is connected between the emitter of the first transistor 11 and the negative terminal of the source to form a closed circuit with the reactive element 12 and lamp 13 at one period of operation of the lighting apparatus as later described. To describe more in detail, the second transistor 14 is so disposed that its collector is connected to the emitter of the first transistor, and its emitter to the negative terminal of the source.

The first and second transistors are so arranged that their bases are alternately supplied with pulse voltage from a control circuit 15 and alternately switched on. The pulse voltage is impressed across respective secondary windings 18 and 19 of pulse transformers l6 and 17 connected between the control electrode or the base and the emitter of the transistors so as to control the transistors.

FIG. 3B shows a modification of the lighting apparatus shown in FIG. 3A wherein thyristors 22 and 23 provided with a controlling electrode are employed as the first and second semiconductor switching elements. Secondary windings 18 and 19 of the pulse transformer are connected between the controlling electrode or gate electrode and the cathode electrode. The parts shown in FIG. 3B identical with those in FIG. 3A are designated by the same reference numerals.

FIG. 4 shows one embodiment of the improved control circuit for controlling the semiconductor switching elements.

The reference numeral 41 indicates a known astable multivibrator. From this astable multivibrator are derived two pulse sequences having rectangular pulses different by 180 in phase and having one-half of pulse duty factor as shown at 51 and 52 in FIGS. 5A and 58. Both output pulse sequences from the astable multivibrator are supplied respectively to a first and a second differentiation circuit 42 and 43. The differentiation circuits are constructed so as to take out only differentiated pulses represented at 53 and 54 in FIGS. 5C and 5D obtained at the time of rising of the rectangular pulses 51 and 52. The construction of such differentiation circuits is well known among those skilled in the art and well not be explained in detail. The differentiated pulses from the differentiation circuit are supplied respectively to a first and a second monostable multivibrator 44 and 45 for triggering them. The monostable multivibrators are so constructed as to generate pulse sequences having pulses 55 and 56 smaller in pulse width than the output pulse from the astable multivibrator as shown in FIGS. 5E and SF when triggered by the differentiated pulses. Consequently, there exists a predetermined time interval 112 between the output pulse 55 from the first monostable multivibrator 44 and the output pulse 56 from the second monostable multivibrator 45. This time interval rb should be selected to be longer than the turn-off time t i.e., the sum of storage time Is and falling time tf, of transistors 11 and 14 shown in FIG. 3A.

Output pulses (shown in FIGS. 5E and SF) of the first and second monostable multivibrators 44 and 45 are supplied respectively to a first and second amplifier 44 and 45. The outputs of amplifiers 46 and 47 are supplied to primary windings 20 and 21 of pulse transformers 16 and 17 and thus, controlling pulses to'switch on the first and second transistors appear across the secondary windings 18 and 19 of the pulse transformers because of inductive coupling.

Now, the operation of the lighting apparatus in the case where the above-mentioned control circuit is used in FIG. 3A will be explained with reference to FIG. 6.

When the first transistor 11 is controlled to be in on-state and the second transistor 14 to be in the off-state under the condition that the DC. source is impressed, charging current Ic of the condenser 12 or lamp current as shown in FIG. 6C flows through discharge lamp 13, and thus the discharge lamp is lighted. After the base current z'b is interrupted by vanishing of the controlling pulse having a definite pulse width, the first transistor 11 is switched off when the turn-off time t has elapsed. Then, both transistors are kept in the off-state during the period tx until the controlling pulse for switching on the second transistor 14 appears. After the lapse of the period tx, the second transistor 14 is switched on by the controlling pulse. As a result, the electric charge stored in the condenser 12 discharges through the second transistor 14 and discharge lamp 13, and discharge current Ic or lamp current as shown in FIG. 6D flows through discharge lamp 13 in the direction reverse to the charging current Ic and consequently, the lamp 13 is kept lighted. After the base current ib is cut off with the interruption of controlling pulse supply and turn-off period t has elapsed, the second transistor is switched off to place both transistors again in the off-state during the period tx. After the lapse of period or the first transistor is again switched on to repeat the above-mentioned operation.

As easily understood from FIG. 6, the period tb indicated in FIG. 5 is represented by the sum of turn-off time t of transistors and period tx. Since the turn-off time of transistors is usually in the order of 5 microseconds, the period rx will be sufficient if it is in the order of 10 microseconds.

The oscillation frequency of the astable multivibrator may be so selected that the switching frequency of the transistors is in the range from several kHz. to several hundred kHz. In case the discharge lamp is lighted at high frequency, the efiiciency of the lamp itself increases and further the stabilizer may be smaller and lighter in weight resulting in a decrease of the electric loss of the stabilizer.

Means for generating two controlling pulse sequences, which present pulses at predetermined time intervals and can maintain two semiconductor elements used in the lighting circuit in the off-state simultaneously as described above, is not limited to that shown in FIG. 4 and other various modifications will be considered.

Other embodiments of the control circuit shown in FIGS. 7 9, and 11 will be explained in the following.

In FIG. 7, the reference numeral 61 indicates an astable multivibrator for generating a pulse sequence having a rectangular pulse 71 as shown in FIG. 8A.

The output pulse of astable multivibrator 61 is supplied to a flip-flop 62, from which are derived two pulse sequences 72 and 73 divided in frequency into one-half and differing by l in phase as shown in FIGS. 8B and 8C. The two pulse sequences from flip-flop 62 are supplied respectively to a first and a second two-input AND circuit 63 and 64, and further the output pulse sequence of the astable multivibrator 61 is supplied to the first and second AND circuits as the other input.

As easily understood, outputs 74 and 75 of the first and second AND circuits 63 and 64 like those shown in FIGS. 8D and 8E are pulse sequences consisting of pulses equal in pulse width to the output of astable multivibrator 61, and there is a.

time interval rb between the two output pulses.

The oscillation frequency and pulse duty factor of the astable multivibrator 61 are so selected that this time lb is greater than the turn-off time t of the transistor. It is not necessary that the pulse duty factor is limited to one-half as shown in the figure.

The output pulse sequences of both AND circuits 64 and 65 are impressed across pulse transformers 16 and 17 through amplifiers 65 and 66 as is the case with the embodiment shown in FIG. 4.

Referring now to FIG. 9, the reference numeral 81 indicates an astable multivibrator for generating rectangular pulses having a positive and a negative voltage level as shown in FIG. 10A. The output pulse of the multivibrator 81 is supplied to an integrator 82 and thus integrated as shown in FIG. 10B. FIG. 10B illustrates an ideal waveform for the integrating operation. The integrated output is supplied to Schmitt circuit 83, which may have threshold levels LP and LM substantially symmetric in positive and negative portions as shown in FIG. 10B, and shaped into the waveform as shown in FIG. 10C. Consequently, the time interval rb occurs between positive pulse 91 and negative pulse 92. The integrator 82 and Schmitt circuit 83 are-adjusted so as to make the time interval tb greater than the turn-off time t of both switching transistors in the same manner as described before.

Subsequently, the output pulses of Schmitt circuit 83 are supplied respectively to a first and a second steering device or rectifiers 84 and 85. The first rectifier 84 is constructed so as to select only positive pulse 91 from the two pulses shown in FIG. C and the second rectifier 85 is constructed so as to select only negative pulse 92.

The positive pulse, which is the output of first rectifier 84, is impressed across the first pulse transformer 16 through a first amplifier 86 in order to drive the first switching element while the negative pulse is reversed in phase by an inverter 87 and then supplied to the second pulse transformer 17 through a second amplifier 88.

Referring now to FIG. 11, the reference numeral 101 indicates a sine wave oscillator. The output of the oscillator 101 is applied to a first and a second steering device comprised, for example, of rectifiers 102 and 103. Only signals of the positive half cycle are taken out by first rectifier 102, and only signals of the negative half cycle are taken out by second rectifier 103 and reversed in phase by an inverter 104. The outputs of the first rectifier 102 and the inverter 104 are impressed respectively to a first and a second Schmitt circuit 105 and 106 each having substantially the same threshold level. Consequently, two pulse sequences having a time interval tb are obtained from both Schmitt circuits as shown in FIGS. 12A and 12B. These pulses are impressed across the pulse transformers l6 and 17 through a first and a second amplifier 107 and 108. It goes without saying that the time interval 1b is selected to be greater than the turn-off time t of the semiconductor switching element as is the case with each embodiment described before.

What we claim is:

I. In apparatus for operating an electric discharge lamp comprising an electric power source, a first semiconductor switching and a reactive impedance element and a discharge lamp which are connected in series across said source, a second semiconductor switching element connected in parallel with the series connection of said reactive impedance element and said discharge lamp, and a control circuit operating said discharge lamp at high frequency by generating two pulse sequences for alternately switching on said first and second semiconductor elements, the improvement wherein said control circuit includes means for providing a time interval greater than the turn-off time of said first and second semiconductor switching elements between pulses of two pulse sequences for alternately switching on said first and second semiconductor switching elements.

2. An apparatus as claimed inclaim 1 wherein said first and second semiconductor switching elements are both transistors.

3. An apparatus as claimed in claim 1 wherein said first and second semiconductor elements are both thyristors.

4. An apparatus as claimed in claim 1 wherein said control circuit comprises an astable multivibrator for generating two pulse sequences different by 180 in phase, a first and a second differentiating means receiving two pulse sequences respectively from said astable multivibrator and deriving differentiated pulses, a first and a second monostable multivibrator for generating in synchronism with said differentiated pulses two pulse sequences of pulses having a pulse width smaller than that of pulses from said astable multivibrator and thereby providing a time interval greater than the turn-off time of said semiconductor switching elements between pulses of two pulse sequences, a first and a second means for amplifying each pulse sequence from said first and second monostable multivibrator, and a first and a second transformer for supplying each amplified pulse sequence from said first and second amplifying means respectively to said first and second semiconductor switchingelements. l

5. An apparatus as claimed in claim 1 wherein said control circuit comprises an astable multivibrator, a flip-flop for receiving an output pulse sequence from said astable multivibrator and generating two pulse sequences different by in phase, a first and a second AND means receiving respectively one of said two pulse sequences and further respectively receiving output pulse from said astable multivibrator to derive two pulse sequences equal in pulse width to the pulse from said astable multivibrator thereby imparting a time interval longer than the turn-off time of said semiconductor switching elements between pulses of the two pulse sequences, a first and a second amplifying means for amplifying output pulse sequences from said first and second AND means, and a first and second transformer for impressing amplified pulse sequences respectively on said first and second semiconductor switching elements.

6. An apparatus as claimed in claim 1 wherein said control circuit comprises an astable multivibrator for generating pulse sequence having a positive and a negative voltage level, an integrating means for integrating the output pulse sequence from said astable multivibrator, and Schmitt circuit having threshold levels substantially symmetric in positive and negative portions and for shaping the output from said integrating means for obtaining a rectangular pulse having a predetermined positive voltage level and a rectangular pulse having a predetermined negative voltage level, a first rectifying means for taking out only pulses having positive voltage level from said Schmitt circuit, a second rectifying means for taking out only pulses having negative voltage level, means for reversing the polarity of negative pulses from said second rectifying means, a first and a second amplifying means for amplifying the output pulse respectively from said reversing means and said first rectifying means, and a first and a second transformer for supplying the output pulses from said first and second amplifying means to said first and second semiconductor switchingelements.

7. An apparatus as claimed in claim 1 wherein said control circuit comprises a sine wave oscillator, a first rectifying means for deriving only portions of positive polarity from the output of said sine wave oscillator, a second rectifying means for deriving only portions of negative polarity, means for reversing the output from said second rectifying means, a first and a second Schmitt circuit having predetermined threshold levels for shaping the outputs respectively from said reversing means and said first rectifying means, a first and a second a'mplifying means for amplifying the outputs respectively of said first and second Schmitt circuits, and a first and a second transformer for supplying the output pulses from said first and second amplifying means respectively to said first and second semiconductor switching elements. 

1. In apparatus for operating an electric discharge lamp comprising an electric power source, a first semiconductor switching and a reactive impedance element and a discharge lamp which are connected in series across said source, a second semiconductor switching element connected in parallel with the series connection of said reactive impedance element and said discharge lamp, and a control circuit operating said discharge lamp at high frequency by generating two pulse sequences for alternately switching on said first and second semiconductor elements, the improvement wherein said control circuit includes means for providing a time interval greater than the turn-off time of said first and second semiconductor switching elements between pulses of two pulse sequences for alternately switching on said first and second semiconductor switching elements.
 2. An apparatus as claimed in claim 1 wherein said first and second semiconductor switching elements are both transistors.
 3. An apparatus as claimed in claim 1 wherein said first and second semiconductor elements are both thyristors.
 4. An apparatus as claimed in claim 1 wherein said control circuit comprises an astable multivibrator for generating two pulse sequences different by 180* in phase, a first and a second differentiating means receiving two pulse sequences respectively from said astable multivibrator and deriving differentiated pulses, a first and a second monostable multivibrator for generating in synchronism with said differentiated pulses two pulse sequences of pulses having a pulse width smaller than that of pulses from said astable multivibrator and thereby providing a time interval greater than the turn-off time of said semiconductor switching elements between pulses of two pulse sequences, a first and a second means for amplifying each pulse sequence from said first and second monostable multivibrator, and a first and a second transformer for supplying each amplified pulse sequence from said first and second amplifying means respectively to said first and second semiconductor switching elements.
 5. An apparatus as claimed in claim 1 wherein said control circuit comprises an astable multivibrator, a flip-flop for receiving an output pulse sequence from said astable multivibrator and generating two pulse sequences different by 180* in phase, a first and a second AND means receiving respectively one of said two pulse sequences and further respectively receiving output pulse from said astable multivibrator to derive two pulse sequences equal in pulse width to the pulse from said astable multivibrator thereby imparting a time interval longer than the turn-off time of said semiconductor switching elements between pulses of the two pulse sequences, a first and a second amplifying means for amplifying output pulse sequences from said first and second AND means, and a first and second transformer for impressing amplified pulse sequences respectively on said first and second semiconductor switching elements.
 6. An apparatus as claimed in claim 1 wherein said control circuit comprises an astable multivibrator for generating pulse sequence having a positive and a negative voltage level, an integrating means for integrating the output pulse sequence from said astable multivibrator, a Schmitt circuit having threshold levels substantially symmetric in positive and negative portions and for shaping the output from said integrating means for obtaining a rectangular pulse having a predetermined positive voltage leveL and a rectangular pulse having a predetermined negative voltage level, a first rectifying means for taking out only pulses having positive voltage level from said Schmitt circuit, a second rectifying means for taking out only pulses having negative voltage level, means for reversing the polarity of negative pulses from said second rectifying means, a first and a second amplifying means for amplifying the output pulse respectively from said reversing means and said first rectifying means, and a first and a second transformer for supplying the output pulses from said first and second amplifying means to said first and second semiconductor switching elements.
 7. An apparatus as claimed in claim 1 wherein said control circuit comprises a sine wave oscillator, a first rectifying means for deriving only portions of positive polarity from the output of said sine wave oscillator, a second rectifying means for deriving only portions of negative polarity, means for reversing the output from said second rectifying means, a first and a second Schmitt circuit having predetermined threshold levels for shaping the outputs respectively from said reversing means and said first rectifying means, a first and a second amplifying means for amplifying the outputs respectively of said first and second Schmitt circuits, and a first and a second transformer for supplying the output pulses from said first and second amplifying means respectively to said first and second semiconductor switching elements. 